This invention relates to a distance measuring apparatus installed on a vehicle for measuring the distance between the vehicle and the one in front.
For example, Japanese Patent Kokai No. 60-49278 discloses a distance measuring apparatus which employs a laser generating element for emitting a laser radiation beam having a constant intensity and a constant range available to measure the distance between the vehicle and the one in front. If the laser beam is set to radiate at a small angle so as to have a long available range, however, a vehicle running at a short distance ahead of the vehicle will deviate from the available range of the laser radiation beam. If the laser radiation beam is set to diverge at a large angle so as to have a short available range, a vehicle running at a great distance ahead of the vehicle will be out of the available range of the laser radiation beam.
Japanese Utility Model Kokai No. 60-76281 discloses a distance measuring apparatus adapted to swing the optical axis of the laser radiation beam emitted from a laser generating element so as to widen the available range of the laser radiation beam. However, it is very difficult to control the optical axis of the laser radiation beam in an appropriate manner since the distance measuring apparatus is subject to great vibrations. It may be considered to widen the available range of the laser radiation beam by providing a plurality of laser generating elements. However, this results in a complex and expensive distance measuring apparatus.